Gear pump



July 25, 1961 w, WE|GERT 2,993,450

GEAR PUMP Filed NOV. lO, 1958 2 SheeS-Shee'l'I l l VEN T0 25 /N 7? W, L Hfbn wa MRT @M40 (Law July 25, 1961 W, WEIGERT 2,993,450

GEAR PUMP Filed Nov. l0, 1958 2 Sheets-Shes?I 2 United States Patent Otce 2,993,450 Patented July 25, 1961 2,993,450 GEAR PUMP Wilhelm Wegert, Stuttgart, Germany, assgnor to Firma Robert Bosch G.m.b.H., Stuttgart, Germany Filed Nov. 10, 1958, Ser. No. 773,070 Claims priority, application Germany Nov. 9, 1957 7 Claims. (Cl. 10S-126) The present invention relates to pumps.

' More particularly, the present invention relates to gear pumps.

In order for gearV pumps to operate with the desired eiciency it is necessary to provide very small spaces around the gears of the gear pump so that there will be a minimum loss of pressure. It is therefore required that the lgears of the :gear pump slide along stationary surfaces, Iand inserts may be located in the pump housing next to the gears to cooperate with the latter to maintain the pressure in the pump. These inserts form a bearing surface against which the gears slide during rotation of the latter, and the inserts are of a softer metal than the relatively expensive gears so that after a certain period of use the inserts become worn and at such time it is possible to remove the worn inserts and replace them with new inserts, the expensive gears of the pump being still useful and undamaged.

Various problems arrive during the wearing away of such inserts. inserts in the pump housing increases, and when this play becomes undesirably large the inserts are changed.

One of the objects of the present invention is to provide a gear pump with an insert arrangement which will automatically compensate for wear of the inserts so as to maintain the gaps around the gears at a minimum as the inserts become worn.

Another object of the present invention is to provide an insert arrangement of the above type which is capable of automatically compensating for both axial and radial wearing away of the inserts so that the inserts are maintained very close to the gears of the pump both axially and radially with respect to the latter even though the inserts become worn during use.

Another object of the present invention is to provide a gear pump with an insert arrangement which will automatically follow the movements of the gears in their bearings during operation so as to maintain or to diminish the gaps. around the gears during operation.

A further object of the present invention is to provide a gear pump composed of simply constructed elements and including a relatively small number of parts which must bemanufactured with a high degree of accuracy.

With the above objects in view, the present invention includes in a gear pump a hollow pump housing having an inlet and an outlet and supporting for rotation a pair of parallel shafts which extend through the hollow interior of the housing. A pair of pump gears are carried by these shafts in the interior of the housing. In accordance with the present invention an insert is located in the pump housing between the latter and the gears at one side of these gears, and this insert is formed with a pair of openings through which the shafts respectively extend and has a peripheral portion extending around the periphery of the pump gears. The peripheral portion of the insert is spaced from the pump housing and the insert is also spaced from the shafts by a certain relativelyV small distance'providing a limited play of the insert' which permits the insert to move in a plane which is normal to the axes of Ilthe shafts. Adjacent to the outlet of the housing the insert yis formed with a recess which has a surface spaced from and directed toward a surface of the housing at the interior thereof, and these surfaces As they become worn the play of thedene between themselves a pressure chamber in which uid under pressure is located for urging the periphery of the insert which is adjacent to the outlet of the housing radially toward the gears.

The novel Ifeatures which are considered as characteristic for the Iinvention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the yfollowing description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a sectional elevational view of a pump according to the present invention taken along line I-I of FIG. 2 in the direction of arrows in a plane which includes the axis of the gears;

FIG. 2 is a transverse sectional view of the structureV of FIG. 1 taken along line lI--II of FIG. 1 -in the direction of arrows;

FIG. '3 is a partly sectional transverse view taken along line -III-III of FIG'. l in the direction of arrows;

FIG. 4 is a transverse sectional view of the structure of FIG. 1 taken along line IV--IV of FIG. 1 in the direction of arrows;

FIG. 5 is a transverse sectional view similar to FIG. 4 of a dierent embodiment of a pump according to the present invention;

FIG. 6' is a fragmentary sectional view of the structure of FIG. 5 taken along line VI--VI of FIG. 5 in the' direction of arrows; and Y FIG. 7 is a force diagram illustrating the operation of the pump of the invention.

Referring now to FIG. l, it will be seen that the pump of the invention includes a housing 1, 2 made up of a hollow member 2 which is closed at its left end and open at its right end, as viewed in FIG. l, and the open\ right end of the member 2 is closed by the housing wall 1. The housing parts 1 and 2 are held together by screw members 4 (FIG. 6), and a pair of diagonally opposed screw members 4 respectively pass through sleeves 3, as is particularly evident from FIG. 6. An elliptical sealing ring 5 is located between the housing parts 1 and 2 so that they are fluid-tightly connected together. TheI housing part 2 is formed with `a pair of parallel bores 7 and 8, andthe cover 1 is formed with a pair of parallel bores 9 and 10 which are respectively coaxial with the bores 7 and 8. A pair of springy closure plates 12 are snapped into the housing 2 at the ends of the bores 7 and 8, respectively, for closing off these bores from the outer atmosphere, and a similar springy plate is snapped into the cover 1 at the outer end of the bore 9 for the sameA purpose. A shaft 13 is turnably supported by the housing 1, 2 in the bores 9 and 7 thereof. This shaft 13 is integral with a pump gear 14 which meshes with la second pump gear 16 which is integral with a shaft 15 which is turnably supported by the bores 8 and 10. The right end of the shaft 15, as viewed in FIG. l, extends outwardly beyond the cover 1 and has a frusto-conical portion 18 adapted to receive a coupling member forming part of a clutch, for example, so that the pump is driven through the transmission member which is carried by the portion 18 of the shaft 15. In this way the gears 14 and 16 are rotatable in the housing 1, 2 without being influenced by any outside forces such as the onesided pull exerted by belt on a pulley, for example, which may be carried by the portion 18 of the shaft 15. Moreover, with this arrangement the pump has a very-i compact construction. A sealing ring 19 is carried by5 the cover 1 around the shaft 15. The pump housing, part 2 is formed, as shown in FIG. 2, with an inlet 20 and with an outlet 21 of a smaller diameter than thel inlet 20.

y 23 is formed with a pair of openings through which the shafts 1'3.a.nd 15 respectively pass, and at these openings the insert 23 is spaced from the shafts by a radial dis, `tance 24. The periphery of the insert 23 is spaced from the inner surface of the housing by the gap 25 shown in FIG. 2, with the exception of the portion of the periphery of. the insert which is adjacent to the outlet 21. The gaps 24 and V25 provide a certain'limited play of the insert 23 in a plane normalrto the axes of the shafts 13V and 15, andthe `extent ofrthis play is limited by the radial dimension of the gap*I 24.; Thus, inaccordance with the radial dimension of theV gap 24 ysurrounding each shaft 13 and 15 the insert23 will be capable of moving transversely of these shafts, Y

Adjacent to the outlet.21 of thepump housing, the insert 23 has a portion 27 which engages an inner-,surface 28-of the housing. This portion 27 of the in ser't is formed with a recess 29 which has agsurface spaced from; and directed toward the vsurface 28 so as to form a pressure chamber with'the latter, and a sealing means in the form of a sealing ring 30 extends along the-outer periphery of the recess29 to seal off this pressure chamber from the rest of the interior* of the housing 1, 2.

The insert 23 is formed with a bore 32 passing through,

a-wall portionuth-ereof coaxially withrtheY outlet21, and

this bore 32 communicates directly with`v the vrecess 29r which forms the pressure chamber: The periphery of the insert 23ls also formed with a bore 33 which is Valigned coaxially with the inlet 20. The-periphery of the insert 23 extends with a relatively small radial clearancefrom the bore 33'around the gears 14 and 16 YupV to the portion 34 of the Ainsert which forms 'approximately one quarter of Vthe'periphery thereof. 'I'his portion' 34 of the insert islocated as close as possible to the lteeth ofl the gears, the distance between the portion 34 of the insertV and the gear teeth being only great enough to permit the gears to turn. Therefore, thev gaps between those teeth of the gearsY which at any givenvinstant are located next to the portion 34 of the insert 23 are substantially closed by the Vinsert portion 34.

The right end fece of the insert z3, as viewed in PIG.V

1, is formed withv a recess 37 which-'communicates with a pair of-arcuate grooves which respectively extendY around the shafts 13 and 15, and as may-be seen from FIG. 3, a sealing member 35 is located in these arcuate grooves and along the periphery of the recess 37 so as to provide a Huid-tight closed pressure recess 37 which is dened by Ithe left surface of the cover 1, as viewed in FIG. 1by the right surface of the insert 23, asviewed in FIG. l, and by the sealing ring 35. As may be seen e from FIG. 3, this recess or chamber 37 is a substantially T-shaped configuration with'the cross bar of the T extending perpendicularly to the shafts 15- and 13 and located at the part of the recess 37v which is nearest to the outlet 21', the leg of the T extending from the cross bar portion thereof toward the inlet 20. The insert 23 is formed with a bore 38 passing from the chamber "37 through the insert to the gears 14 and 16 at the pressure side-thereof'located at theY pressure chamber 39 ofthe pump which communicates with the bore 32, as indicated in FIG. 2.

k'I'he dish-shaped insert 23 is open at itsY left end,las viewed in FIG. 1, and in accordance with the presentv invention a springy closure V plate means is provided' for closing thisopen v.end of the insert 23. In the embodiment of FIGS. 1-4, this ,closure plate means vtakes the form theV rings 41 and 42, respectively,; -is1equal to .the largest f permissible shifting movement ofi the. insert; 23.

In other words, these radial-distances are equaljtofthe radial distances 24. Thus, the'ring's 41- 42-serve`-tolimit the movement of the insert 23 to-the" right, as viewed in Fig. 4. At their portions of smallest cross section the rings 41 and 42 are formed with the slits 43, respectively,

so that these rings operate asfsprings. The rings 4I and 42 have attened surface portions engagingeach other as indicated in FIG; 4 so that in this way the positions of the rings 41 and 42 with respect to eachother are determined. Along not quite half of 'itspeiiphery the insert 23 -is spaced by the gap 44Y (FIG. 4) from the rings 41 and 42 particularly in the region of the slits 43 thereof, this gap 44 having a radial' dimension' corresponding tothe radial distance between the'gears' 14 and 16, on theV one hand, andthe periphery of the shell or insert 23. As is evident from FIG. l, the rings 41 andV` 42 extend to the left, as viewed in FIG. 1, beyond'the insert-23mm recesses of ythe housing part Y2: These recesses are in fact a single common recess, and` only the right vportions of the rings- 41 and 42, as viewed in FIG. 4, press against the housing part 2. The :left portions'of the rings 41 and 42, as viewed in FIG. 4, press only `against-the insert23, so that the latter is in lthis way -urged to theA left, as Vviewed inV FIG. 4, by the springyclosure plate-means'41 and;

42; It is evident that the rings l41 and 42 serve `to substantially close the dish-shaped insert 23 at the left side thereof, as viewed in FIG. l. Thus, the springy rings 41 and 42urge the insert 23 against the inner surface 2S of the housing 1; 2'. Each of the rings- 41'and`42 carries a sealing ring 45 located between each ring andV the housingA 2, as indicated in FIG. l.

The shaft 13'is formed wither-axial bore 47 extending this bore 48 terminates and communicateswith a' radial bore 49 leading to Ithe chamber 55. The 'plates- 12 Yformwith the ends of the shaft 13 and the left "end of the shaft v 15 the chambers 51, 52 and 53.` The chamber 53communicates-through the bore 47 with theY chamber 51, and this -chamber 51 communicates through aVv passage S4 formed in the housing part 2 with the chamber 52 Whichcommunicates through the bore 48 and the radial passage e 49 with theV chamber 55. This chamber 55 communicates through an uni-llustrated passage formedin the housing .1, 2 withY the suction side of-the pump.

When the Ypump is operated soas topurnpd` a huid such as oil, yfor example, the oi-l is sucked into the pump through the inlet 20 and lthe bore 33 ofeithe'einsert23,A and the pump transfers this oil in the 4gapsabetween thei teeth of the` gears 14 and 16 to the pressureside ofltheA pump where the oil is discharged under pressure through"y the outlet passages 32 and 21. The axial play of the. gears 14 and 16 with respect totheinsert 23,on the oneV hand, and the closure platemeans 41,V 42, onfthe other= hand, is maintained ata minimum, first asva result .of theY inherent elasticity of the sealing ring 35 which urges* Ithe insert 23 `to the left, as viewed in FIG. l, and second tenete-the portion 34 ofthe insert z3. While the teeth of the gear move along thevportion 34 of the in- 23 they build up the pressure in the oil which exists-at .the outletof the pump.- The smaller the axial and radial gaps at the portion 34 of the insert the-greater is the volumetric efficiency of the pump. As the pressure of the uid in the pump increases at the pressure chamber 39 the pressure of the iiuid in the gaps between the teeth next to the portion 34 of the insert 23 also increases and tends to shift the gears 14 and 16 to the right, as viewed in FIG. 2. However, this pressure at the outlet side of the pump also prevails in lthe uid within the pressure ychamber 29, and thus the pressure acts on the insert 23 to urge .the latter toward the inlet of the pump. In this way the radial gap between the portion 34 of the insert 23 and the gears 14 and 16 remains at all times the same and there is no decrease in efficiency resulting from an increase in this radial gap. The shiftability of the insert 23 is dependent upon the yieldability of the'springy rings 41 and 42, and the latter areso constructed'that the insert 23 and the gears 14 and 16 shift to the same extent, so that the radial play between the gears 14 and 16 and the portion34 of the insert 23 remain Vthe same under all operating conditions of the pump. It is also possible to provide a reduction in the size of the radial gap between portion 34 and the insert 23 and the gears 14 and 16 with increasing pressure at the outlet of the pump. It is only necessary to limit the shift; ing ofthe insert 23 Within the housing 2 to such an extent that the sealing ring 30 can reliably maintain the pressure chamber 29 sealed oi from the gap 25 in the interior of the pump housing even if the insert 23 has shifted slightly to the right, as viewed in FIG. 2.

As was pointed out above, the shifting movement of the insert 23 is limited by the radial distance between the shafts 13 and 15 and the insert 23, on the one hand, and by the radial distance between these shafts and the rings 41 and 42. Thus, when the rings 41 and 42 and the insert 23 bear against the shafts 13 and 15, the insert 23 has moved through the maximum permissible distance, and it is necessary at this time to replace the worn insert 23 with a new insert.

It will be noted that the forces in the chamber 29 acting to the right on the insert 23 at the portion 34 thereof, as viewed in FIG. 2, are directed oppositely to the forces which act on the portion 34 of the insert 23 to urge the latter toward the left, as viewed in FIG. 2, and as a result these forces have no tendency to distort the insert 23. Therefore,there is no change in the radial gap between the gears 14 and 16 and the portion 34 of the shell 23 as a result of the forces acting on the portion 34 of the shell 23.l

It will also be noted that the uid which is under pressure 'at the outlet of the pump acts only on the relatively small inner surface 28 of the pump housing. 'Ihe oil does not exert any larger forces on the housing. Thus, with the pump of the invention the pump housing need only have a sufficient mass and stiffness to withstand the normal stresses exclusive of the maximum pressure of the fluid acting against the surface 28. If this latter surface should change its shape slightly as a result of the pressure of the uid, there will be no decrease in the efficiency of the pump and therefore when designing the pump the mass of the housing thereof need not be made so great as to entirely resist the pressure of the fluid at the discharge side of the pump.

All of the forces and moments acting on the insert 23 compensate each other and balance each other under all operating conditions. The axial pressure on the insert 23 lexerted by the oil in the gaps between the teeth of the gears which are next to the portion 34 of the insert 23 are directly opposed by the pressure in the T-shaped recess 37. These opposed forces have no tendency to tilt the insert 23 in the housing, since these opposed lforces 'are-directly in line with each other.

In the radial direction the Jforce of the oil under pressure in the chamber 29 tends to move the insert 23 to the right, as viewedin FIG. 2. f This -force is opposed by a pair of forces.- Thus, there is the force of the oil at the right side of the portion 34 of the insert 23, as viewed in FIG. 2, and also there Iis the force of the springs 41 and 42.. The resultants of all of these forces will act in a horizontal plane normal to the plane of FIG. 2 and located midway between the-axes of the gears 14 and v16, respectively. The shape and location of the surface of the recess 29 which is directed toward'the surface 28 is such that the resultant ofthe forces ofi the oil under pressure in the pressure chamber 29 will be spaced from the pair of opposed forces inversely to the size of these vforces so as to eliminate -any tendency of theinsert 23 to tilt as a result of the radial forces. Thus, referring to FIG. 7 which may beconsidered 4as taken in a horizontal plane normal to the plane of FIG. 2 and midway between the axes of the gears 14 Vand 16, it can be assumed that the force F1 represents thefforce of the oil under pressure in the gap between the teeth of the gears 14 and 16 located just to the right of the portion 34-of theV insert 23 and urging the latter to the left. 'Ihe force F2 represents the force of the springs 41 and 42, these forces F1 and Fzbeing the resultant forces of the oil under pressure and the springs which urge the insert 23 to the left, as viewed in FIG. 2. It will be noted that these two forces F1 and F2 are spaced from each other, land this space will be somewhat greater than one half the thickness of each -gear 14 and 16. The resultant of the forcesof the oil under pressure in the chamber 29 is shown at F3, and it will be noted that the distance a of the force F3 from the larger resultant force F1 is smaller than the distance b of the force F3 from the smaller resultant force F2. As a result, the force F2 multiplied by the distance b will equal the force F1 multiplied by the distance a, and therefore there will be no tendency for the insert 23 to tilt as a result of the radial forces shown in FIG. 7. Thus, it can be seen that the distance of the force F3 from the forces F1 and F2 is inversely proportional to the size of the forces F1 and F2.

As is indicated'in dot-dashlines in FIG. l, the opening 32 is offset with respect to the recess 29 so as to provide the action of the forces indicated in FIG. 7.

Some fof the oil under pressure in the gaps between th'e teeth of the gears 14 and 16 will reach the shafts 13 and 15 and ow axially along the outer surface thereof through the openings 7-10 of the housing 1, 2 so that Vin this way t-he Vrotary movement of the shafts is lubricated. This very small amount of oil will reach the chambers 51-53 and 55'. The oil which collects in the chamber 53 will tiow along vthe bore 47 of the shaft 13 to the chamber 51 and Will flow together with the oil which has already collected in the chamber 51 throughthe passage 54 to the chamber 52 to be joined therewith with the oil already collected therein. All of the oil in the chamber 52 ows along the bore 48 to the radial bore 49 and from the latter into the chamber 55, and the oil which collects in the chamber 55 flows 4back to the suction side of the pump through the unillus- Vtrated passage which provides communication between the chamber 55 and the suction side of the pump.

The embodiment of the invention which is illustrated in FIGS. 5 and 6 differs from that of FIGS. 1-4v only with respect to the construction of 4the insert 60, which corresponds to the insert 23, and the closure plate means 61, 62 which corresponds to the closure plate means 41, 42. The remaining parts of the structure of FIGS. 5 and 6 are identical with those of FIGS. l4 and are indicated with the same reference characters. The plane in which the section of FIG. 5 is taken is located to the -left of the plane ofFIG. 4 in FIG. l, so that FIG. 5 shows the configuration of the housing part 2 at the portion thereof which cooperates with the rings 41 and 42,

Vand it will be noted from FIG. 5 that the rings 41 and `42 will only press atftheiriight.- sides, as kviewed in 4,V against the housing part 2 and their left sides will only,` press against theinsert 23.

Referring now to FIGS. 5 and 6, the insert 60 has a peripheral portion which extends beyond the gears 14 and16 only along the outlet side ofthe pump.; In this way the closure plate members 61 and 62 are capable of pressing against the left peripheral portion of the insert 60, as viewed in FIG. 5. Spring members 63 serve to urge the rings 61' and 62V against the insert 60. Each of the spring members 63 is in the form of asteely band and. is composed of a pair of'Y arcuate portions interconnected at their ends, and the outer arcuate portion is split approximately at its center, as shown in FIG. 5, so that each springy. member 63 has a pair of free springy ends located adjacentI to but. spaced from Yand directed towardweach other. These; springy members 63 are smaller than the plates 61 and 62 and are respectively located in recesses'of these plates. As is apparent from FIG. 6, the recesses which receive the springs 63 do not extend all the wayy upto the gears 14 and 16, so that the springs 63 areY in this way maintained spaced from the gears 14 andv 16. These springs 63 provide the action that the'members 41 and 42 provide, and with the embodiment of FIGfS the rings 61 and 62. need not be provided witheccentrically located bores.

Of course, thefstructure of the invention also can be used to function as a motor rather than avpump, and in this case the only difference would be thatrthe oil would flow through themotor in the reverse direction and the gears would rotate in a reverse direction as compared tothe operation of the structure as a pump.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in otherV types of pumps differing from the types described above.

While the invention has been illustrated and described as embodied in gear pumps, it is not intended to be limited to the details shown, since various modifications and structural changes '-may be made Without departing in any way from the spiritY of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for varions` applications without omitting features that, from the: standpoint of prior art, fairly constitute essential characeristics of the genericl or specicaspects of this invention and, therefore, suchadaptations should and are intended to be comprehended within the meaning and 'grange of equivalence ofthe following claims.

VWhat is claimed as new and desired to be secured by Letters Patent is:

1'. In a gear pump, in combination, a hollow pump housing having an inlet and an outlet; a pair of parallel shafts turnably carried by said housing and extending across'the hollow interior thereofra-pair of pump gears respectively carried 'by said shafts and located in the hollow` interior of said housing; a substantially dishshaped insert located between said housing and gears and having a base portion extending at one side of the latter normal to Vthe axes thereof and formed with a pair of openings through'whioh said shafts respectively extend, said base portion covering the entire side faces of said gears-atsaid one side' thereof, said insert having a peripheral portion integral with said base portion and extend- -ing'completely around the periphery of said gears and spaced :from said housing and said insert also being spaced 'from isaid shafts so that said/-inserthas a limited play 1in saidlhousing in a plane normal to the axes of said shafts; said insert having a pressure surface spaced from and directed toward a surface of said housing at the outletof the latter land deningwith the latterghousing sur- 'facea pressure chamber Yinrwhich fluidv under pressure'is located, Vsaidinsert having oppositeA said pressure surface a sealing- 4 surface directed toward?I the periphery` of said 'gearsand' urged" by said-duidlpressuref-inf. said pressure '8 chamber against the periphery of said gears with a pressure depending exclusively on the pressure of the uid. 1nv said pressure chamber, said pressure chamber; com-r municating with the outlet of said housingfandwithsaid.

gears on theV pressure side thereof; and closure. plate meansY located next to the oppositeside. of said gears and substantially closing said dish-shaped insert.4

2. In a gear pump, in combination, a hollow pumpv housing having an inlet and -an outlet; a pair of parallel shafts turnably supported by said housing kand'extending through the hollow interior thereof; a pair of pump gears carried by said shafts and locatedin the hollow interior of saidhousing; a substantially dish-shaped insert located in saidy housing between the latter and said gears and havinga base portion extending at one side of said gears normal to the axes thereof, said base portion covering theentire side faces of said gears atsaid one side thereof.` said insert having a peripheral portion integral with said base portion and extending completely around the periphery of said gears and spaced from said Vhousing and said insert having a pressure surface directed toward and spaced from a surface of said housing intheY interior thereofadjacent said outlet thereof and defining with the latter housing surface apressure chamber in which fluid under pressure is located, said insert having opposite said pressure surface a sealing surface directed toward the periphery of said gears vand urged by said iluid pressure in said pressure chamber against the periphery of said gears-with a pressure depending exclusively on the pressure of the uid in said pressure chamber, said pressure chamber communciatng with the outlet of said housing and with said gears on the pressure side thereof; and closure plate -means engaging said gears at the opposite side'thereof and closing substantially the space surrounded by the periphery of said insert, said shafts being spaced at the sides thereof which are directed toward the outlet of'said housing from said insert and said closure plate means by a distance which limits the movement of said insert'in said housing in a direction normal to the axis of each shaft.

3. In a gear pump, in combination, a hollow pump housing having an inlet and an outlet; a pair of parallel shafts turnably carried byV said housing and extending through the hollow interior thereof; a pair of pump gears v carried by said shafts and located in the interior of said housing; a substantially dish-shaped insert located in said housing between the latter and said gears and having a base portion extending at one side thereof normal to the axes thereof and formed with openings through which said shafts pass, said base portion covering the entire side faces of said gears at said one side thereof, said insert having a peripheral portion integral with said base portion and extending completely around the periphery of said gears and also spaced from said housing, said insert having a portion directed toward the outlet of said housing and formed with a recess having a pressure surface directed toward and spaced from a surface of the housing in' the interior thereof and defining with the latter' housing surface a pressure chamber in which fluid under pressure is located, said insert having opposite said pressure surface a sealing surface directed toward the periphery of said gears and urged by said fluid pressure in said pressure chamber against the periphery of said gears wit-h a pressure depending exclusively on the pressure of the fluid in said pressure chamber, said pressure chamber communicating with the outlet of said housing and with said gears on the pressure side thereof; and springy `closure plate Imeans located in said housing against the other side of said gears and cooperating with said insert for resiliently urging said portion thereof toward said surface of said housing, said closure plate means yielding to permit movement of said insert in a direction away fromr the outlet of said housing. Y

4. In a gear pump. asrecited inclaim 3, s aid springy closure plate means being in the form of a pair of split rings respectively extending around said shafts.

5. ln a gear pump as recited in claim 3, said springy closure plate means including a pair of rings through which said shafts respectively pass, said rings respectively being formed with recesses extending from peripheral portions thereof which are nearest to said inlet of said housing into said rings, and springs located in said Iecesses and engaging said rings and housing for urging said rings away from said inlet toward said outlet so as to urge said insert at said portion thereof toward said surface of said housing.

6. In a gear pump, in combination, a hollow pump housing having an inlet and an outlet; a pair of parallel shafts turnably carried by said housing and extending through the hollow interior thereof; a pair of pump gears carried by said shafts and located in said housing; a substantially dish-shaped insert located in said housing between the latter and the gears and having a base portion extending at one side of said gears normal to the axes thereof, said base portion covering the entire side faces of said gears at said one side thereof, said insert having a periphery extending around said gears and spaced from said housing, said insert also being spaced from said shafts so that said insert has a limited play in said housing in a plane normal to the axis of said shafts, said insert having adjacent the outlet of said housing a pressure surface directed toward an inner surface of said housing and defining with the latter inner surface a pressure chamber in which fluid under pressure is located, said insert having opposite said pressure surface a sealing surface directed toward the periphery of said gears and urged by said fluid pressure in said pressure chamber against the periphery of said gears with a pressure depending exclusively on the pressure of the uid in said pressure chamber, said pressure chamber communicating with the outlet of said housing and with said gears on the pressure side thereof, and the uid under pressure in said pressure chamber acting on said insert with a resultant force directed from said outlet toward said inlet substantially midway between the axis of said shafts; and closure plate means located against said gears at the other side thereof and cooperating With said insert for urging the latter in a direciton opposite to said resultant force, the uid under pressure in the gaps between the teeth of said gears and said closure plate means acting on said insert with a pair of resultant forces which are spaced from each other and located in the same plane as said rst-mentioned resultant force substantially midway between the axis of said shafts, the distance between said first-mentioned resultant force and said pair of resultant forces being inversely proportional to the size of said pair of resultant forces.

7. In a gear pump, in combination, a pump housing having an inlet and an outlet; a pair of parallel shafts turnably supported by said housing and extending through the interior thereof; a pair of meshing pump gears fixed to said shafts, respectively, and located in the interior of said housing; a cup-shaped insert located in said housing and having a base portion extending substantially normal to the axes of said shafts, being located -in said housing at one side of said gears and covering the entire side faces of said gears at said one side thereof and a peripheral portion integral With said base portion and extending completely around the periphery of said gears, said base portion being formed with openings through which said shafts respectively extend, said base portion being spaced from said shafts and said peripheral portion being spaced from the periphery of said gears and said pump housing by a distance providing limited movement of said insert with respect to said housing and shafts in a plane normal to the axes of said shafts, said peripheral portion of said insert having a pressure surface spaced from and directed toward a surface of said housing at said outlet thereof and dening with the latter housing surface a pressure chamber in which fluid under pressure is located, said peripheral portion having opposite said pressure surface a sealing surface directed toward the periphery of said gears and urged by said uid pressure in said pressure chamber substantially into sealing contact against the periphery of said gears in the region of said pump outlet with a pressure depending exclusively on the pressure of the iiuid in said pressure chamber, said base portion having an outer side thereof directed away from said gears and toward the surface of said housing in the interior thereof; and an endless sealing member located between said surfaces of said base portion of said insert and said housing and defining with the latter an additional pressure chamber in the region of said outlet, said insert being formed with a passage providing communication between said additional pressure chamber and the pressure side of said gears for introducing iluid under pressure into said additional pressure chamber to urge said base portion of said insert substantially into sealing contact With said side faces of said gears.

References Cited in the le of this patent UNITED STATES PATENTS 164,147 Conver June 8, 1875 1,880,108 Ross Sept. 27, 1932 2,742,862 Banker Apr. 24, 1956 2,816,510 Jarvis Dec. 17, 1957 2,817,297 Mosbacher Dec. 24, 1957 2,824,522 Compton Feb. 25, 1958 2,824,524 Banker Feb. 25, 1958 2,837,031 Ilune June 3, 1958 2,842,066 Hilton July 8, 1958 2,855,854 Aspelin Oct. 14, 1958 2,936,717 Kalle May 17, 1960 FOREIGN PATENTS 625,405 Germany Feb. 8, 1936 771,050 Great Britain Mar. 27, 1957 782,701 Great Britain Sept. l1, 1957 `1,165,651 France June 2, 1958 

